Termination and reduced gel in high cis polybutadiene

ABSTRACT

The present invention is directed to a process for forming a high-cis polydiene. The process includes catalyzing a diene polymerization, and terminating the polymerization with a termination mixture comprising an inorganic base and at least one of an amine and a carboxylic acid. The catalyst system is a mixture of (a) organoaluminum compounds; (b) organonickel compounds; and (c) fluorine-containing compounds. The use of an inorganic base reduces the amount of more expensive amine necessary to effectively terminate the polymerization as well as reducing the corrosion in the reaction container. The use of an inorganic base with a carboxylic acid results in a very low gel content as well as reducing the corrosion in the process systems.

FIELD OF THE INVENTION

This invention relates to diene polymerization, particularly to high-cisdiene polymerization. More particularly, the present invention relatesto a high-cis, low gel polydiene and a process for producing the same.

BACKGROUND OF THE INVENTION

High cis polydienes have been prepared using an organonickel basedcatalyst system. The use of the organonickel based catalyst system canresult in a rapid rate of polymerization, and the ability to controlvarious polymer properties by varying the catalyst ratios. Moreover,organonickel based catalyst systems are generally hardy catalysts thatmay be able to maintain catalytic activity at a wide range ofpolymerization conditions. The use of organonickel catalysts to formhigh cis polydienes relies on the need for a fluorine-containingco-catalyst, such as HF or BF₃. These co-catalysts, however, may becumbersome to work with as they tend to generate strong acids whencontacting water, leading to possible equipment corrosion and possiblegel-formation of the polymer. Moreover, the reaction products of theco-catalysts include trialkylboranes when BF₃ is used, which can reactwith molecular oxygen to form peroxyboranes, compounds that mayspontaneously homolytically break to form radicals, increasing the gelcontent upon aging of the finished products.

A variety of terminators, including water, alcohols, polyols, amines,and carboxylic acids have been used to terminate nickel-catalyzed dienepolymerizations. Although such terminators may be effective in thetermination of the diene polymerization, the protic solvents are capableof reacting with fluoride containing compounds in the polymerizationmixture, generating strong acids, which may lead to corrosion problemsin the finishing equipment and can also lead to cationic coupling(gelation) of the finished polymer.

Amine termination is another method that has been used in previoussyntheses of high-cis polydienes, with the amine acting as a base toneutralize. any acidic compounds in the polymerization mixture, reducingcorrosion and cationic gellation. The bases thus formed also react withtrialkylboranes to form Lewis acid-Lewis base complexes. These complexesreduce the reactivity of trialkylboranes toward oxygen, thus reducingthe generation of radicals, which leads to gel formation. Unfortunately,such amine terminators are often quite, expensive, thus increasing thecost of the overall process.

It would thus be desirable to develop a system for terminating thesynthesis of high-cis polydienes that would be capable of overcoming theincreased gel content and/or equipment corrosion experienced with theabove, mentioned termination systems while maintaining or reducingcosts.

SUMMARY OF THE INVENTION

The present invention is directed to a process for forming a high-cispolydiene. The process includes catalyzing a diene polymerization, andterminating the polymerization with a termination mixture comprising aninorganic base and at least one of an amine and a carboxylic acid.

In another embodiment, the present invention is directed to a polymercomposition including a high-cis polydiene terminated with an inorganicbase and at least one of an amine and a carboxylic acid. The polydienepreferably has a cis content greater than about 85-90% and a static gelcontent less than about 5%.

In a third embodiment, the present invention is directed to a processfor producing high-cis polydienes. The process includes a continuouspolymerization of a nickel catalyzed polydiene terminated by atermination mixture comprising sodium hydroxide and at least one of anamine and a carboxylic acid.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

A process for forming a high-cis polydiene composition is provided. Theprocess includes catalyzing a polydiene polymerization, followed bytermination with a termination mixture comprising an inorganic base. Thecatalyzation of the polymerization reaction is preferably carried outwith a catalyst system including at least one organonickel compound, atleast one organoaluminum compound, and at least one fluorine-containingcompound. A termination mixture is used to terminate the polymerization.The inclusion of an inorganic base, such as NaOH, to the terminationmixture provides for the neutralization of acidic byproducts oftenformed during the polymerization and termination reactions, therebyreducing corrosion to the vessels and equipment used in thepolymerization process. The use of an inorganic base also reduces theamount of more expensive compounds in amine termination reactions.

The resultant high-cis polydiene composition preferably has a ciscontent greater than about 85%, more preferably greater than about 92%.The composition has a static gel content that is preferably less than5%, more preferably less than 1.0%.

The component of the catalyst of this invention which contains nickelmay be any organonickel compound. It is preferred to employ a solublecompound of nickel. Thus, nickel salts of carboxylic acids and organiccomplex compounds of nickel are suitable. These soluble nickel compoundsare normally compounds of nickel with a mono- or bi-dentate organicligand containing up to 20 carbons. “Ligand” is defined as an ion ormolecule bound to and considered bonded to a metal atom or ion.Mono-dentate means having one position through which covalent orcoordinate bonds with the metal may be formed; bi-dentate means havingtwo positions through which covalent or coordinate bonds with the metalmay be formed. By the term “soluble” is meant soluble in inert solvents.Thus, any salt of an organic acid containing from about 1 to 20 carbonatoms may be employed. Representative of organonickel compounds arenickel benzoate, nickel acetate, nickel naphthenate, nickel octanoate,bis(alpha-furyl dioxime)nickel, nickel palmitate, nickel stearate,nickel acetylacetonate, nickel salicaldehyde, bis(salicylaldehyde)ethylene diimine nickel, bis(cyclopentadienyl) nickel,cyclopentadienylnickel nitrosyl and nickel tetracarbonyl. The preferredcomponent containing nickel is a nickel salt of a carboxylic acid or anorganic complex compound of nickel, such as a nickel boroacylate inwhich the acyl group is derived from the organic acids cited above.

By the term “organoaluminum compound” it is meant any organoaluminumcompound corresponding to the formula:

 Al R₁(R₂)(R₃)

in which R₁ is selected from the group consisting of alkyl (includingcycloalkyl), aryl alkaryl, arylalkyl, alkoxy, and hydrogen; R₂ and R₃being selected from the group of alkyl (including cycloalkyl), aryl,alkaryl, and arylalkyl. Representative of the compounds corresponding tothe formula set forth above are diethyl aluminum hydride, di-n-propylaluminum hydride, di-n-butyl aluminum hydride, diisobutyl aluminumhydride, diphenyl aluminum hydride, di-p-tolyl aluminum hydride,dibenzyl aluminum hydride, phenylethyl aluminum hydride, phenyl-n-propylaluminum hydride, p-tolyl ethyl aluminum hydride, p-tolyl n-propylaluminum hydride, p-tolyl isopropyl aluminum hydride, benzyl ethylaluminum hydride, benzyl n-propyl aluminum hydride, and benzyl isopropylaluminum hydride and other organoaluminum hydrides. Also included aretrimethyl aluminum, triethyl aluminum, tri-n-propyl aluminum,triisopropyl aluminum, tri-n-butyl aluminum, triisobutyl aluminum,tripentyl aluminum, trihexyl aluminum, tricyclohexyl aluminum, trioctylaluminum, triphenyl aluminum, tri-p-tolyl aluminum, tribenzyl aluminum,ethyl diphenyl aluminum, ethyl di-p-tolyl aluminum, ethyl dibenzylaluminum, diethyl phenyl aluminum, diethyl p-tolyl aluminum, diethylbenzyl aluminum and other triorganoaluminum compounds. Also included arediethylaluminum ethoxide, diisobutylaluminum ethoxide anddipropylaluminum methoxide.

Another component of the catalyst system employed in this invention is afluorine containing compound. The fluorine may be supplied by hydrogenfluoride, boron trifluoride, or by hydrogen fluoride and borontrifluoride being complexed with a member of the class consisting ofmonohydric alcohols, phenols, water, mineral acids containing oxygen,water, aldehydes, esters, ethers, ketones and nitriles.

The ketone subclass can be defined by the formula R′COR where R′ and Rrepresent a alkyl, cycloalkyl, aryl, alkaryl and arylalkyl radicalscontaining from 1 to about 30 carbon atoms; R′ and R may be the same ordissimilar. These ketones represent a class of compounds which have acarbon atom attached by a double bond to oxygen. Representative but notexhaustive of the ketones useful in the preparation of the borontrifluoride and hydrogen fluoride complexes of this invention areacetone, methyl ethyl ketone, dibutyl ketone, methyl isobutyl ketone,ethyl octyl ketone, 2,4-pentanedione, butyl cycloheptanone,acetophenone, amylphenyl ketone, butylphenyl ketone, benzophenone,phenyltolyl ketone, quinone and the like. Typical complexes of theketones are boron trifluoride.acetophenone and borontrifluoride.benzophenone, also hydrogen fluoride.acetophenone andhydrogen fluoride.benzophenone and hydrogen fluoride.acetone.

The aldehyde subclass can be defined by the formula R—CHO where Rrepresents an alkyl, cycloalkyl, aryl, alkaryl and arylalkyl radicalcontaining from 1 to about 30 carbon atoms. The aldehydes have a carbonatom attached to an oxygen atom by means of a double bond.Representative but not exhaustive of the aldehydes are butyraldehyde,anisaldehyde, cinnamic aldehyde, isobutyraldehyde, heptaldehyde,dodecylaldehyde, benzaldehyde, phenylacetaldehyde, tolualdehyde,m-nitrobenzaldehyde, p-nitrobenzaldehyde, m-hydrobenzaldehyde and thelike. Typical complexes formed from the aldehydes are borontrifluoride-benzaldehyde, boron trifluoride-tolualdehyde, hydrogenfluoride-benzaldehyde and hydrogen fluoride-tolualdehyde.

The ester subclass can be represented by the formula R′—COOR where R′and R are represented by alkyl, cycloalkyl, aryl, alkaryl, and arylalkylradicals containing from 1 to about 30 carbon atoms. The esters containa carbon atom attached by a double bond to an oxygen atom.Representative but not exhaustive of the esters are ethyl butyrate,ethyl octanoate, isopropyl hexanoate, amyl acetate, hexyl propionate,cetyl acetate, ethyl benzoate, amyl benzoate, phenyl acetate, phenylbutyrate, phenyl benzoate and the like. Typical complexes formed fromthe esters are boron trifluoride-ethyl benzoate and borontrifluoride-phenyl acetate; also hydrogen fluoride-ethyl benzoate, andhydrogen fluoride-phenyl acetate.

The ether subclass can be defined by the formula R—O—R where each Rindependently represents an alkyl, cycloalkyl, aryl, alkaryl andarylalkyl radical containing from 1 to about 30 carbon atoms.Representative but not exhaustive of the ethers are ethoxybutane,ethoxyoctane, isopropoxyhexane, propoxyhexane, ethoxybenzene,amyloxybenzene and the like.

The nitrile subclass can be represented by the formula RCN wherein Rrepresents an alkyl, cycloalkyl aryl, alkaryl, and arylalkyl. Thenitriles contain a carbon atom attached to a nitrogen atom by a triplebond. Representative but not exhaustive of the nitrile subclass areacetonitrile, butyronitrile, acrylonitrile, benzonitrile, tolunitrile,phenylacetonitrile, and the like. Typical complexes prepared from thenitrites are boron trifluoride.benzonitrile, and hydrogenfluoride.benzonitrile.

The monohydric alcohol subgroup of the above class of compounds can besymbolically portrayed as ROH where R represents an alkyl, cycloalkyl,and an arylalkyl radical containing from 1 to 30 carbon atoms.Representative, but not exhaustive of the alcohol group, are methanol,ethanol, n-propanol, isopropanol, n-butanol, benzyl alcohol, and thelike. Typical complexes formed from the above groups are as follows:BF₃.methanol, BF₃.ethanol, BF₃.butanol, BF₃.n-hexanol HF.methanol,HF.butanol and HF.hexanol.

The phenol subgroup of the above class of compounds can be symbolicallyportrayed as Φ-OH wherein Φ represents a benzenoid group. Representativebut not exhaustive of the phenol group are phenol, p-cresol, resorcinol,naphthol, hydroquinone and the like. Typical complexes formed from theabove phenol subgroup are as follows: BF₃·2-phenol, BF₃·p-cresol,HF.p-cresol and HF.phenol.

A number of the members in the subgroup mineral acids containing oxygenwill complex with BF₃ and HF. Representative but not exhaustive of themineral acid subgroup are phosphoric acid, sulfuric acid, nitric acidand the like. The preferred complexes formed from the mineral acidsubgroup are BF₃·100% phosphoric acid and BF₃·85% phosphoric acid, andHF·100% phosphoric acid.

Water, although in a subgroup by itself, forms at least two hydratecomplexes. These are BF3·H₂O and BF₃·2H₂O.

When not available commercially, many of the boron trifluoride complexescan be readily formed by directly contacting boron trifluoride gas, (acolorless gas at ordinary temperatures and pressures) with the compoundused as the complexing agent, that is, the electron donor compound. Thiscontact is accomplished with a reacting apparatus combined with asensitive weighing mechanism in order to achieve the desired mole ratiosbetween the BF₃ and the electron donor compound. The reaction is carriedout under an inert atmosphere. The reaction environment may consist onlyof the reacting components, BF₃ gas, and the electron donor compound, orwhen convenient, the reaction may be carried out in the medium of aninert organic diluent. This last condition is usually necessary when theelectron donor compound exists as a solid and must be put into solutionor suspension to insure adequate contact with the BF₃ gas.

The various boron trifluoride complexes vary greatly in their shelf lifestability. Some, for example, BF₃·isopropanol are quite unstable indaylight at room temperature. Others, for example, BF₃·phenol are quitestable and possess a relatively long shelf life at room temperature.Where the particular BF₃ complex, specified as a catalyst component,possesses an unstable shelf life, it should be prepared as near to thetime of polymerization as feasible.

Hydrogen fluoride is a limpid liquid which fumes strongly in air, isvery poisonous, forms ulcerated sores if it comes in contact with theskin, and is very dangerous to handle or to manipulate. By complexingthe hydrogen fluoride with the complexing agents heretofore mentioned,some of the advantages of this invention are a safer, easier and moreaccurate way of handling the hydrogen fluoride component of the catalystsystem. Hydrogen fluoride complexes usually have a lower vapor pressureand do not fume as badly as does hydrogen fluoride. Hydrogen fluorideboils at 19.7° C., whereas a 40% by weight of hydrogen fluoride diethylether azeotrope boils at 74° C. When the hydrogen fluoride is complexed,the corrosiveness of the hydrogen fluoride is reduced. The hydrogenfluoride complex can be dissolved in a solvent and thus can be handledand charged to the system as a liquid solution. The solvent which can beemployed may be an alkyl, alkaryl, arylalkyl or an aryl hydrocarbon.Benzene, for example, is a convenient solvent system.

The complexes of this invention are usually prepared by simplydissolving appropriate amounts of the complexing agent, for instance, aketone, an ether, an ester, an alcohol, a nitrile or water, in asuitable solvent and an appropriate amount of the hydrogen fluoride in asuitable solvent and mixing the two solvent systems. The mixing of thecomplexing agents, except water, should be done in the absence of watervapor. Another possible method would be to dissolve either the hydrogenfluoride or the complexing agent in a suitable solvent and adding theother component. Still another method of mixing would be to dissolve thecomplexing agent in a solvent and simply bubble gaseous hydrogenfluoride through the system until the complexing agent is reacted withhydrogen fluoride. The concentrations may be determined by weight gainor chemical titration. The amount of complexing agent cannot bespecifically set down. The amount of complexing agent may be a rangedepending on the conditions of the reaction system, the hydrogen bondingstrength of the complexing agent, the size of the complexing agent, orit may be an equilibrium between the hydrogen fluoride complex and thehydrogen fluoride plus the complexing agent.

When the fluorine containing compound is derived from boron; trifluorideor a boron trifluoride complex, the optimum concentration from any onecatalyst component changes from that when HF is employed, since borontrifluoride contains three atoms of fluorine, and thus the molar ratioof the catalyst components will be different. For instance, when theorganoaluminum compound (Al) to the organonickel compound (Ni) rangesfrom about 0.3/1 to about 500/1, and when the mole ratio of the borontrifluoride complex prepared by complexing boron trifluoride with amember of the class consisting of esters, aldehydes, ketones andnitriles (BF₃ complex) to the organonickel compound (Ni) ranges fromabout 0.3/1 to about 500/1, the mole ratio of the organoaluminum (Al) tothe BF₃ complex ranges from about 0.1/1 to about 4/1.

The preferred Al/Ni mole ratio ranges from about 1/1 to about 150/1; thepreferred BF₃ or BF₃ complex/Ni mole ratio ranges from about 1/1 toabout 150/1; and the preferred Al/BF₃ complex mole ratio ranges fromabout 0.3/1 to about 1.4/1.

When the fluorine containing compound is derived from hydrogen fluorideor a hydrogen fluoride complex, the polymerization activity issuccessful over a wide range of catalyst concentrations and catalystratios. The three catalyst components interact to form the catalystcomponents. As a result, the optimum concentration or any one catalystcomponent is very dependent upon the concentration of each of the othertwo catalyst components. Furthermore, while polymerization will occurover a wide range of catalyst concentrations and mole ratios, polymerhaving the most desirable properties are obtained over a more narrowrange.

Polymerization can occur while the mole ratio of the organoaluminumcompound (Al) to the organonickel compound (Ni) ranges from about 0.3/1to about 300/1; the mole ratio of HF or hydrogen fluoride complex (HFC)to the organonickel compound (Ni) ranges from about 2/1 to about 300/1and the mole ratio of hydrogen fluoride complex to the organoaluminumcompound ranges from about 0.2/1 to about 15/1. However, the preferredmole ratios of Al/Ni ranges from about 2/1 to about 80/1, the preferredmole ratio of HF or HFC/Ni ranges from about 5/1 to about 100/1 and thepreferred mole ratio of HF or HFC/Al ranges from about 0.4/1 to about7/1. The concentration of the catalyst employed depends on factors suchas purity, rate desired, temperature and other factors, therefore,specific concentrations cannot be set forth except to say that catalyticamounts are used. Although not intended to be limiting, a specificexemplary catalyst combination suitable for polymerizing butadiene inhexane to produce elastomers having desirable properties according tothe present invention includes from 0.010-0.020 mmoles nickelboroacylate, 1.0-2.0 mmoles BF₃ and 1.0-1.5 mmoles tri-isobutly aluminumper 100 g butadiene.

The catalyst system may optionally include an alcohol component. Thealcohol component is preferably selected from the group consisting of C₂to C₂₀ alcohols, or more preferably n-hexanol or n-octanol, and mixturesthereof. It may be preferred to coordinate an alcohol component to afluoride compound.

Suitable dienes for use in preparation of the subject high cis, low gelpolydiene include conjugated dienes. C₄-C₈ conjugated diene monomers arethe most preferred. Preferred conjugated diene monomer units areselected from the group consisting of 1,3-butadiene, 1,3-pentadiene,2,4-hexadiene, isoprene, and mixtures thereof. Especially preferred are1,3-butadiene monomer units.

The polymerization may optionally include additional monomer units, suchas vinyl substituted aromatic hydrocarbon monomer units. Where included,preferred vinyl substituted aromatic hydrocarbon monomer units areselected from one or more of styrene, a-methyl-styrene, 1-vinylnaphthalene, 2-vinyl naphthalene, vinyl toluene, methoxystyrene,t-butoxystyrene, and the like, as well as alkyl, cycloalkyl, aryl,alkaryl, and aralkyl derivatives thereof, in which the total number ofcarbon atoms in the combined hydrocarbon is generally not greater thanabout 18, as well as any di- or tri-vinyl substituted aromatichydrocarbons, and mixtures thereof.

The polymerization may be carried out by any methods known in the art.The preferred method of the invention involves continuously feeding themonomer and catalyst streams to a polymerization reactor. This can beaccomplished by continuously and separately feeding the monomer andcatalyst streams to the reactor. However, it is often preferred to firstblend the monomer and catalyst streams together prior to injection intothe polymerization reactor. It should also be noted that while not apreferred procedure, it may be possible to employ the in-situ method ofcatalyst composition addition by separately injecting the organonickelcompound, the organoaluminum compound and the fluorine-containingcompound into the reactor.

The polymerizations of this invention are conducted in an inerthydrocarbon solvent and are consequently solution polymerizations. Theterm “inert solvent” means that the solvent does not enter into thestructure of the resulting polymer, does not adversely affect theproperties of the resulting polymer and does not adversely affect theactivity of the catalyst employed. Suitable hydrocarbon solvents whichmay be employed include aliphatic, aromatic or cycloaliphatichydrocarbons such as hexane, pentane, toluene, benzene, cyclohexane andthe like. The preferred hydrocarbon solvents are aliphatic hydrocarbonsand of these hexane is particularly preferred.

The solvent/monomer volume ratio may be varied over a wide range. From4:1 to 10:1 volume ratio of solvent to monomer can be employed.Suspension polymerization may be carried out by using a solvent, e.g.,butane or pentane, in which the polymer formed is insoluble. It shouldbe understood, however, that it is not intended to exclude bulkpolymerizations from the scope of this application.

The polymerizations of the invention should be carried out under aninert atmosphere such as nitrogen and precautions should be taken toexclude materials such as water and air which will deactivate thecatalyst components.

Once a desired conversion is achieved, the polymerization can beterminated with a termination mixture comprising an inorganic base and anoncoupling type of terminator that inactivates the catalyst, such aswater, an acid, a lower alcohol, and the like or with a coupling agent.An antioxidant such as 2,6-di-tert-butyl-4-methylphenol may be addedalong with, before or after the addition of the terminator. Terminatorssuitable for use in the termination mixture with the inorganic base inthe present invention include amines as well as water, alcohols, polyolsand carboxylic acids. Particularly preferred termination mixturesinclude an inorganic base with at least one amine and/or carboxylicacid.

Inorganic bases suitable for use in the termination mixture of thepresent invention include any inorganic base capable of deactivating thecatalyst components as well as neutralizing acidic byproducts producedduring polymerization while not detrimentally reacting with the polymerchains. Nonlimiting examples of suitable inorganic bases includeinexpensive bases such as hydroxides, carboxylates and carbonates ofvarious metals. A preferred inorganic base is NaOH. A second preferredinorganic base is NaCO₃.

A particularly preferred termination mixture for use in the presentinvention includes an inorganic base in an amine-water mixture. When amixture of water and an amine are used to terminate the polymerization,the water reacts with the organoaluminum compounds and/or fluorinecontaining compounds to deactivate the catalyst components, leaving theamine available to react with the trialkylboranes. The use of anamine-water mixture is detailed in commonly assigned copending U.S.patent application Ser. No. 10/208,520, filed Jul. 30, 2002 now U.S.Pat. No. 6,596,825, entitled “Low Gel High Cis Polydiene”, thedisclosure of which is incorporated herein by reference. The inorganicbase can be used to-neutralize the acidic byproducts of the terminationand polymerization reactions. This allows for the addition of less amineand reduces or eliminates corrosion in the reaction vessel by raisingthe pH of the system.

The inorganic base/amine/water mixture may be added in conjunction or inseries. It is preferred that the mixture be added in series. Thepreferred molar ratio of amine:water is about 1:100, more preferablyabout 1:500. The water component of the termination mixture mayadditionally include an alcohol. Preferred alcohols are one or more ofmethanol, ethanol, isopropanol, propanol, and butanol. When included, apreferred water:alcohol ratio may be about 1:500, more preferably about1:50. Alternately, the water can be omitted from the termination mixturesuch that the termination mixture includes only an amine/inorganic basemixture.

Suitable amines include ammonia, ammonium hydroxide, primary amine,secondary amine, tertiary amine, aliphatic amine and aromatic amine.Exemplary amines include, but are not limited to, pyridine, aniline,benzylamine, n-butylamine, cyclohexylamine, diethylamine,diisopropylamine, dimethylamine, diphenylamine, ethylamine,ethylenediamine, hexamethylene diamine, N,N-diethylcyclohexylamine,N,N-dimethylcyclohexylamine, N,N,N′-trimethyl ethylene diamine,N,N,N′N′-tetramethyl ethylene diamine (TMEDA); and substituted pyridinessuch as N,N-dimethylaminopyridine (DMAP), 4-pyrrolidinopyridine, and4-piperidinopyridine. TMEDA is particularly preferred as the aminecomponent of the termination mixture, with or without the use of water.

A second preferred termination mixture includes a carboxylic acid and aninorganic base. The inorganic base includes those described above.Suitable carboxylic acids include those represented by the formula

wherein R is selected from the group consisting of alkyl, cycloalkyl andarylalkyl substituted or unsubstituted containing from 3 to 20 carbonatoms. A preferred carboxylic acid for use in the termination mixture is2-ethyl hexanoic acid (EHA) A metal salt of a carboxylic acid may alsobe added to the termination mixture. Thus, another preferred terminationmixture includes a mixture of EHA and the calcium salt of EHA. As withthe amine based termination mixture described above, water may or maynot be included in the carboxylic acid based termination mixture. Again,the inorganic base is thought to react with acid byproducts believed tobe produced during polymerization as well as any acidic products thatmay result from residual water reacting with the EHA or other carboxylicacid used.

When used with both the amine and the carboxylic acid, the amount ofinorganic base added to the reaction mixture is preferably enough tomaintain the pH in the reaction vessel above 7. Preferably, an amount ofinorganic base is added to adjust the pH to about 7-9. Although notintended to be limiting, a suitable amount for use in the presentinvention is an amount equal to the molar equivalent of the F⁻ ionspresent in the reaction mixture from the addition of BF₃ or otherfluorine catalyst compound. The use of the inorganic base in thetermination mixture reduces the amount of amine necessary to effectivelyterminate the polymerization.

Regardless of the exact composition of the termination mixture, thepolymer cement is then transferred to a blend tank, where it is storeduntil such time as it is desolventized in a manner known by thoseskilled in the art, such as a hot water stripping system.

When the polymerization reaction has been stopped, the polymer can berecovered from the polymerization mixture by conventional procedures ofdesolventization and drying. For instance, the polymer may be isolatedfrom the polymerization mixture by coagulation of the polymerizationmixture with an alcohol such as methanol, ethanol, or isopropanol, or bysteam distillation of the solvent and the unreacted monomer, followed byfiltration. The polymer product is then dried to remove residual amountsof solvent and water (if present). The polymer product can be driedusing any conventional method such as vacuum drying, drum drying,extruder drying, steam water desolventizing and the like.

The polymer is continuously withdrawn from the polymerization reactor atthe same rate as the monomer and catalyst stream are fed to the reactor.Steady state conditions are reached after three (3) residence cycles. Atthis time, the polymer can be removed from the reactor at the same rateas the monomer and catalyst streams are being fed to the reactor.

The final product is a high-cis, low gel polydiene. The polydienepreferably has a cis content greater than about 85%, more preferablygreater than about 90%. The gel content of the final product ispreferably less than about 20%, more preferably less than about 10%. Thestatic gel content of the final product is preferably less than about10%, more preferably less than about 5%. The use of EHA/water/NaOH as atermination mixture leads to extremely low static gel contents ofgenerally less than 2%. The weight-average molecular weight (M_(W)) ofthe final product is preferably between about 60,000 and 600,000, morepreferably between about 100,000 and 450,000, and most preferablybetween about 150,000 and 400,000.

The high cis low gel polydienes formed in conjunction with the presentinvention may find uses in a variety of applications. For example, thepolymer obtained may be employed in rubber uses that require mechanicalcharacteristics and abrasion resistance, for example, tire, hose, belt,golf ball, plastics modification and other various industrialapplications.

It is frequently desirable to include other additives known in the artto the compositions of the present invention. Suitable additives includestabilizers, antioxidants, conventional fillers, processing aids,accelerators, extenders, curing agents, reinforcing agents, reinforcingresins, pigments, fragrances, and the like. Other additives known in theart are also contemplated for use in the present invention. Specificexamples of useful antioxidants and stabilizers include2-(2′-hydroxy-5′-methylphenyl) benzotriazole, nickeldi-butyl-di-thiocarbamate, tris(nonylphenyl) phosphite,2,6-di-t-butyl4-methylphenol, and the like. Exemplary conventionalfillers and pigments include silica, carbon black, titanium dioxide,iron oxide, and the like. Suitable reinforcing materials are inorganicor organic products of high molecular weight. Examples include glassfibers, asbestos, boron fibers, carbon and graphite fibers, whiskers,quartz and silica fibers, ceramic fibers, metal fibers, natural organicfibers, and synthetic organic fibers. These compounding ingredients areincorporated in suitable amounts depending upon the contemplated use ofthe product, preferably in the range of about 1-350 parts of additivesor compounding ingredients per 100 parts of the high cis low gelpolydiene.

EXAMPLES

The invention is described more fully based on the following examples asset forth herebelow. However, the invention should be in no wayconstrued as to be limited by these examples.

Samples of high-cis polybutadiene were prepared using reactant amountsas set forth in table 1. Various termination mixtures were used to stopthe reaction. Sample 1 corresponds to a TMEDA termination. Sample 2corresponds to a water/TMEDA termination. Samples 3-7 correspond toEHA/NAOH/water termination. As seen in table 1, the use of anEHA/NaOH/water termination mixture resulted in a polymer having a staticgel content of less 1.3% in all instances, and substantially lower thana polymer terminated with a TMEDA or TMEDA/water mixture without NaOH.Microgel is a measure of the area of a GPC scan after filtration of thedissolved sample compared to the area of a similar standard polymer ofknown gel content.

Static gel is the amount of polymer which does not dissolve in tolueneafter sitting for 48 hours, without agitation.

TABLE 1 Nickel Hi-Cis Termination Examples Sample No. 1 2 3 4 5 6 7Hexane Rate (pounds/hour) 37,619 37,619 131 100 100 106.5 95.5 Butadiene(BD) Rate 10,000 10,000 25 25 25 25 25 (pounds/hour) Ni mmoles/100 g BD0.06 0.06 0.08 0.08 0.08 0.03 0.06 Triisobutyl Aluminum 1.3 1.3 3.482.38 2.49 2.011 1 mmoles/100 g BD BF3 mmoles/100 g BD 1.43 1.43 3.292.52 3.27 1.819 1.8 Peak Reaction Temperature 245 245 205 235 222 215235 (° F.) TMEDA mmoles/100 g BD 1.7 1.7 0 0 0 0 0 EHA mmoles/100 g BD 00 9.85 8.91 9.84 10.75 8.13 Water mmoles/100 g BD 0 800 72.14 60.0971.65 593 593 Sodium Hydroxide mmoles/100 g BD 0 0 10.96 9.18 10.8511.29 8.54 Mooney Viscosity (ML4 + 1 @ 56.3 49.3 54.5 45 35.7 46 30.8100° C.) Mooney T-80 (seconds) 16.7 13.1 7.3 4.7 5.9 5.2 10.5 Mn 5805062645 84507 73113 71460 78413 48781 Mw 204463 226598 367471 326761308720 329017 215266 Microgel 13.00% 9.00% 6.00% Static Gel 17.60% 3.70%0.60% 0.90% 1.30% 0.10% 0.00%

The invention has been described with reference to the exemplaryembodiments. Modifications and alterations will occur to others uponreading and understanding the specification. The invention is intendedto include such modifications and alterations insofar as they comewithin the scope of the disclosure and claims.

We claim:
 1. A process for forming a high-cis polydiene, the processcomprising the steps of: a. catalyzing a diene polymerization, and b.terminating the polymerization with a termination mixture comprising aninorganic base and at least one of an amine and a carboxylic acid. 2.The process of claim 1 wherein said catalyzing is carried out by acatalyst system comprising at least an organonickel compound, anorganoaluminum compound, and a fluorine-containing compound.
 3. Theprocess of claim 2 wherein said organonickel compound is selected fromthe group consisting of nickel benzoate, nickel acetate, nickelnaphthenate, nickel octanoate, bis(alpha-furyl dioxime)nickel, nickelpalmitate, nickel stearate, nickel acetylacetonate, nickelsalicaldehyde, bis(salicylaldehyde) ethylene diimine nickel,bis(cyclopentadienyl) nickel, cyclopentadienylnickel nitrosyl, nickeltetracarbonyl, nickel boroacylate, and mixtures thereof.
 4. The processof claim 2 wherein said organoaluminum compound is selected from thegroup consisting of trimethylaluminum, triethylaluminum,triisobutylaluminum, tri-n-butylaluminum, trihexylaluminum, and mixturesthereof.
 5. The process of claim 2 wherein said fluorine-containingcompound is boron trifluoride or a boron trifluoride complex prepared bycomplexing boron trifluoride with a member selected from the groupconsisting of monohydric alcohols, phenols, water, mineral acidscontaining oxygen, aldehydes, esters, ethers, ketones and nitriles. 6.The process of claim 2 wherein said fluorine-containing compound ishydrogen fluoride or a hydrogen fluoride complex prepared by complexinghydrogen fluoride with a member selected from the group consisting ofmonohydric alcohols, phenols, water, mineral acids containing oxygen,aldehydes, esters, ethers, ketones and nitriles.
 7. The process of claim2 wherein said catalyst system further comprises one or more alcohols.8. The process of claim 1 wherein said diene polymerization comprisesthe polymerization of diene monomer units.
 9. The process of claim 8wherein said diene monomer units are conjugated diene monomer units. 10.The process of claim 9 wherein said conjugated diene monomer units areselected from the group consisting of 1,3 butadiene, 1,3-pentadiene,2,4-hexadiene, isoprene, and mixtures thereof.
 11. The process of claim1 wherein said termination mixture further comprises water.
 12. Theprocess of claim 1 wherein said inorganic base is selected from thegroup consisting of NaOH and NaCO₃.
 13. The process of claim 1 whereinsaid amine compound is selected from the group consisting of TMEDA,triethylamine, diethylamine, and mixture thereof.
 14. The process ofclaim 1 wherein said inorganic base is added in an amount such that saidtermination reaction is conducted under conditions with a pH of 7 orgreater.
 15. The process of claim 11 wherein the ratio of amine compoundto water is about 1:500.
 16. The process of claim 15 wherein said ciscontent is greater than about 92%.
 17. The process of claim 15 whereinsaid static gel content is less than about 5%.
 18. The process of claim17 wherein the static gel content is about 2% or less.
 19. The processof claim 1 wherein said polydiene includes polybutadiene monomer units.20. The process of claim 1 wherein said carboxylic acid is 2-ethylhexanoic acid.
 21. The process of claim 1 wherein said terminationmixture comprises a carboxylic acid and a metal salt of a carboxylicacid.
 22. The process of claim 21 wherein said termination mixturecomprises 2-ethyl hexanoic acid and a calcium salt of 2-ethyl hexanoicacid.
 23. The process of claim 2 wherein said inorganic base is presentin an amount at least equal to the molar equivalent of the F⁻ ionspresent in the fluorine containing compound.
 24. A process for producinghigh-cis polydienes comprising a continuous polymerization of nickelcatalyzed polydiene terminated by a termination mixture comprisingsodium hydroxide and at least one of an amine and a carboxylic acid. 25.The process of claim 24 wherein said termination mixture furthercomprises water and said amine is selected from the group consisting oftertiary amines, TMEDA, triethyl amine, tripropyl amine, and mixturesthereof.
 26. The process of claim wherein said termination mixturecomprises sodium hydroxide, 2-ethyl hexanoic acid and a calcium salt of2-ethyl hexanoic acid.